In the prior art, a user equipment (User Equipment, UE) reports a network resource identifier (Network Resource Identifier, NRI) to a radio network controller (Radio Network Controller, RNC) in an initial direct transfer message which is used for sending a routing area update (Routing Area Update, RAU) request message; then, the RNC reports a routing area identifier (Routing Area Identifier, RAI) and the NRI to a mobile switching center (Mobile Switching Center, MSC); and finally, the MSC sends them to a target mobility management entity (Mobility Management Entity, MME) or a target SGSN, so that the target MME or the target SGSN determines, according to the RAI and the NRI, a source SGSN where the UE is located, and obtains a context of the UE from the source SGSN.
When the RNC initiates a reverse single radio voice continuity (Reverse Single Radio Voice Call Continuity, SRVCC) handover (in other word, a handover from a circuit switched domain (Circuit Switched Domain, CS domain) to a packet switched domain (Packet Switched Domain, PS domain), normally the RAI and NRI reported by the UE are sent to the MSC in a relocation required (Relocation Required) message. In the reverse SRVCC handover process, the target MME or the target SGSN obtains the context of the UE from the SGSN where the UE is located.
Generally, addressing information of an SGSN may use an RAI FQDN structure, e.g., <NRI>.<RAC>.<LAC>.<MNC>.<MCC>.3gppnetwork.org. Evidently, the addressing information includes RAI, NRI, and the like, so that the target MME or the target SGSN may be connected, by using the above addressing information, to the source SGSN where the UE is located. The RAI consists of a mobile country code (Mobile Country Code, MCC), a mobile network code (Mobile Network Code, MNC), a location area code (Location Area Code, LAC), and a routing area code (Routing Area Code, RAC).
However, after a UE initiates a CS call (such as a voice call), if the UE supports a reverse SRVCC handover, the UE will initiates an RAU process when an RNC initiates a reverse SRVCC handover, so that the RNC may obtain an NRI of the UE from an initial direct transfer message (such as an RAU request message), and ensure that an RAI of the UE and an RAI of a cell where the UE is located are consistent. When the RNC initiates the reverse SRVCC handover, the RAI and the NRI are carried in a relocation required message and are sent to an MSC, and then the MSC sends them to a target MME or a target SGSN. When the RNC fails to be connected to a source SGSN, the RNC will select another SGSN; therefore, the NRI reported by the UE is invalid. If the UE is in a CS connected state, after a inter-RNC handover of the UE, the UE initiates an RAU process after the handover, and sends an RAU request message through an uplink direct transfer (Direct Transfer) message, thereby ensuring an RAI of the UE and an RAI of a cell where the UE is located are consistent. However, the uplink direct transfer message does not include an NRI. When an SGSN where the UE is located is changed, the RNC still cannot obtain addressing information of a new source SGSN.
Or if a UE is in a PS connected state, after a inter-SGSN handover of the UE, if an RAI is changed, under the circumstances that the RNC does not inform the UE of a new RAI, the RNC cannot obtain an RAI of a source SGSN where the UE is located after the handover. Even if the RNC notifies the RAI change to the UE, because the RAI is changed, the UE will initiate an RAU process after receiving the notification, so that the UE obtains a new RAI. However, when the SGSN where the UE is located is changed, the UE uses an UPLINK DIRECT TRANSFER message to send an RAU request, where the message does not carry an NRI. Even if an NRI is carried, it is also possible that the RNC cannot select an SGSN indicated by the NRI, that is, the NRI is changed. Therefore, the RNC still cannot obtain addressing information of a new source SGSN.